package day15;

/**
 * @author oldliu
 * @since 1.0
 */
public class Circle {

    public static class Ball{
        private double r;

        public double getR() {
            return r;
        }

        public void setR(double r) {
            this.r = r;
        }
        public double area(){
            return Math.PI*r*r*4;
        }
    }
}
